Optical connector with tilted mirror

ABSTRACT

A light coupling unit for use in an optical connector includes a waveguide alignment member that receives and aligns at least one optical waveguide. The light coupling unit includes a light redirecting member that has an input surface configured to receive input light from the end face of the optical waveguide. A curved reflective surface of the light redirecting member receives light from the input surface propagating along an input axis and redirects the light such that the redirected light propagates along a different redirected axis. An output surface of the light redirecting member receives the redirected light and transmits the redirected light as output light propagating along an output axis and exiting the light redirecting member. A curved intersection of the curved reflective surface and a first plane formed by the input and redirected axes has a radius of curvature. The curved reflective surface has an axis of revolution disposed in the first plane. The axis of revolution forms a first angle with the redirected axis which is non-zero. The waveguide alignment member is configured such that the end face of the optical waveguide is positioned at a location that is not a geometric focus of the curved reflective surface.

BACKGROUND

Optical connectors can be used for optical communications in a varietyof applications including telecommunications networks, local areanetworks, data center links, and internal links in computer devices.Expanded optical beams may be used in connectors for these applicationsto provide an optical connection that is less sensitive to dust andother forms of contamination and so that alignment tolerances may berelaxed. The optical connector is generally considered an expanded beamconnector if there is an expanded beam at a connection point. Generally,an expanded beam is a beam that is larger in diameter than the core ofan associated optical waveguide (usually an optical fiber, e.g., amulti-mode fiber for a multi-mode communication system). The expandedbeam is typically obtained by diverging a light beam from a source oroptical fiber. In many cases, the diverging beam is processed by opticalelements such as a lens or mirror into an expanded beam that isapproximately collimated. The expanded beam is then received by focusingof the beam via another lens or mirror.

BRIEF SUMMARY

A light coupling unit for use in an optical connector includes awaveguide alignment member that receives and aligns at least one opticalwaveguide. The light coupling unit includes a light redirecting memberthat has an input surface configured to receive input light from the endface of the optical waveguide. A curved reflective surface of the lightredirecting member receives light from the input surface propagatingalong an input axis and redirects the light such that the redirectedlight propagates along a different redirected axis. An output surface ofthe light redirecting member receives the redirected light and transmitsthe redirected light as output light propagating along an output axisand exiting the light redirecting member. A curved intersection of thecurved reflective surface and a first plane formed by the input andredirected axes has a radius of curvature. The curved reflective surfacehas an axis of revolution disposed in the first plane. The axis ofrevolution forms a first angle with the redirected axis which isnon-zero. The waveguide alignment member is configured such that the endface of the optical waveguide is positioned at a location that is not ageometric focus of the curved reflective surface.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic cross-sectional view of an optical connectoraccording to some embodiments;

FIGS. 2A and 2B depict an elliptical cross section of a reflectorillustrating the relationship between the geometrical focus and thereflective surface in accordance with some embodiments;

FIG. 3A shows a schematic cross-sectional view of a connector assemblyaccording to one aspect of the disclosure;

FIG. 3B shows a perspective schematic view of light paths through theconnector assembly of FIG. 3A;

FIGS. 4A and 4B are schematic diagrams that illustrate ray-tracing of alight coupling unit;

FIGS. 5A and 5B are schematic diagrams showing ray tracing of a portionof an example light coupling unit in accordance with some embodiments;

FIG. 6A shows a schematic perspective view of a unitary light couplingunit 600 according to one aspect of the disclosure; and

FIG. 6B shows a schematic perspective view of a connector assemblyaccording to one aspect of the disclosure.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The disclosure generally relates to individual optical waveguides, setsof optical waveguides such as optical fiber ribbons, and opticalconnectors useful for connecting individual optical waveguides ormultiple optical fibers such as in optical fiber ribbon cables. Theoptical connectors discussed herein incorporate a light coupling unitthat can combine the features of optical waveguide alignment, along withredirecting and shaping of the optical beam. The optical connectorsdiscussed in some embodiments are expanded beam connectors. In someembodiments, the light coupling unit is a unitary structure which may bea molded piece. Optical connector embodiments discussed herein mayprovide for reduced insertion loss, reduced optical aberrations, such ascoma aberration, and/or reduced back reflection.

FIG. 1 shows a schematic cross-sectional view of an optical connector190 according to some embodiments. The optical connector 190 comprisesat least one light coupling unit 100 disposed within a housing 110. Thecross-sectional view presented in FIG. 1 is on an XZ plane of an XYZCartesian coordinate system, such that the XZ plane passes through acentral axis 122 of an optical waveguide 120.

The optical waveguide 120 is received and aligned by a waveguidealignment member 115 of the light coupling unit 100. The opticalwaveguide 120 is received and aligned within the waveguide alignmentmember 115 such that the optical waveguide end face 124 faces an inputsurface 132 of a light redirecting member 130 of the light coupling unit100. In some embodiments, the waveguide alignment member 115 isconfigured such that the end face 124 of the optical waveguide 120 ispositioned at a location that is not the geometrical focus of the curvedreflective surface 134 as discussed in more detail below. In some cases,the light redirecting member 130 can comprise a solid medium that istransparent to the wavelength of light input from the optical waveguide120 and has an index of refraction that is greater than one. In somecases, the optical waveguide end face 124 can be immediately adjacentthe input surface 132 of the light redirecting member 130; however, insome cases the optical waveguide end face 124 can be set back slightlyfrom the input surface 132, e.g., through the use of waveguide stopfeatures (not shown). An index matching material can be disposed betweenthe waveguide end face 124 and the input surface 132, optically couplingthe optical waveguide 120 to the input surface 132. In some cases, thelight redirecting member 130 can include a reflective surface of ahollow cavity formed in the light coupling unit 110.

The optical connector 190 is configured to mate with a mating opticalconnector (not shown in FIG. 1) along a mating direction. According tosome aspects, the mating direction is not parallel with the central axis122. To readily accomplish the mating, the connector housing 110 furtherincludes a mating surface 112 and alignment features 114, 116. Thealignment features 114, 116, align the output surface 136 of the lightredirecting member 130 within the optical connector, to one of either asecond light coupling unit in a second optical connector (not shown), ora transceiver such as an optical detector or emitter, such as a verticalcavity surface emitting laser (VCSEL). In one particular embodiment, anoptional recessed mating surface 113 can be formed such that a pocket160 can be formed proximate the output surface 136, so that an air gapcan be formed between the output surface 136 and the adjacent secondoptical connector or transceiver. In one particular embodiment, theunitary light coupling unit 100 can be a hermaphroditic coupling unit,such that the first 100 and a second unitary light coupling unit (notshown), can be identical and attached to each other, as describedelsewhere. In one particular embodiment, at least one of the inputsurface 132 and the output surface 136 can include an antireflectivecoating, and/or can be proximate an index matching material.

The waveguide alignment member 115 can comprise a groove extending alonga groove direction for receiving and aligning the optical waveguide 120,as described, for example, in PCT Publication Nos. WO2013/048730entitled OPTICAL CONNECTOR HAVING A PLURALITY OF OPTICAL FIBRES WITHSTAGGERED CLEAVED ENDS COUPLED TO ASSOCIATED MICROLENSES; WO2013/048743entitled OPTICAL SUBSTRATE HAVING A PLURALITY OF STAGGERED LIGHTREDIRECTING FEATURES ON A MAJOR SURFACE THEREOF; and in U.S. PatentApplication Ser. Nos. 61/652,478 entitled OPTICAL INTERCONNECT (AttorneyDocket No. 67850US002, filed May 14, 2013), and 61/710,083 entitledOPTICAL CONNECTOR (Attorney Docket No. 70227US002, filed Sep. 27, 2013)which are incorporated herein by reference. In some cases, the groovedirection can be parallel to and aligned with the central axis 122. Insome cases, the waveguide alignment member 115 can instead comprise acylindrical hole (not shown) capable of receiving and aligning anoptical waveguide 120 which can be an optical fiber. The opticalwaveguide 120 can be any suitable waveguide including, for example, aplanar waveguide, a single mode optical fiber, or a multimode opticalfiber. In some cases, the optical waveguide 120 is a multimode opticalwaveguide suitable for wavelengths in a range from about 600 nanometersto about 2000 nanometers. In one particular embodiment, the opticalwaveguide 120 can have a circular cross-sectional profile. In somecases, the optical waveguide can instead have a polygonalcross-sectional profile.

The light redirecting member 130 includes the input surface 132 forreceiving input light 140 along an input axis 142 from the opticalwaveguide 120, a curved reflective surface 134 for reflecting thereceived input light 140 as a redirected light 150 propagating along adifferent redirected axis 152, and an output surface 136 for receivingthe redirected light 150 and transmitting the redirected light 150 as anoutput light 155 propagating along the output axis 156. The inputsurface 132 can be a planar surface that is substantially perpendicularto the input axis 142 and/or substantially parallel to the redirectedaxis 152 in some embodiments. The output surface 136 can be a planarsurface that is substantially parallel to the input axis 142 and/orsubstantially perpendicular to the redirected axis 152 in someembodiments.

In FIG. 1, the redirected axis 152 is shown to be within a first plane(i.e., the XZ plane) of the XYZ Cartesian coordinate system, and theinput axis 142 and redirected axis 152 form a redirection angle ϕbetween them. The redirection angle ϕ can be any desired angle suitablefor the application, and can be, for example, more than 90 degrees, orabout 90 degrees, or less than 90 degrees, e.g., about 80 degrees, orabout 70 degrees, or about 60 degrees, or about 50 degrees, or about 40degrees, or about 30 degrees, or even less than about 30 degrees. In oneparticular embodiment shown in FIG. 1, the redirection angle ϕ is about93 degrees. In some cases, the central axis 122 of the optical waveguide120 can be coincident with the input axis 142; however, in some casesthe optical waveguide 120 can be aligned to the input surface 132 sothat the input axis 142 and the central axis 122 form an angle betweenthem (not shown) as might be caused by refraction at the waveguide endfacet or the input surface of the light coupling unit.

In some embodiments, the axis of revolution 106 is disposed at a firstangle, α1, with respect to the input axis 142 and is disposed at asecond angle, α2, with respect to the redirected axis 152 and/or theoutput axis 156. In some cases α1=α2 and in some cases α1≠α2. Forexample α1 and α2 can be between about 40 degrees and about 50 degrees.In some implementations, α1=α2=45 degrees. In some cases, the lowestaberration and the lowest insertion loss are achieved when α1=α2.

In some embodiments, the output axis 152 may be oriented at a 90 degreeangle with respect to the input axis 142 as illustrated in FIG. 1. Ingeneral, the output axis 152 and the input axis 142 may be oriented atnon-90 degree angles to one another. The input light 140 has a firstdivergence half-angle, θi, where the first divergence half-angle θi isbetween about 3 degrees and about 10 degrees, or between about 5 degreesand about 8 degrees, or about 7 degrees.

The redirected light 150 can be substantially collimated within thelight coupling unit 100. The redirected light 150 has a seconddivergence half-angle θo that can, in some cases, be a convergencehalf-angle θo, where the second divergence is less than the firstdivergence. In some cases, the second divergence or convergencehalf-angle θo is less than about 5 degrees, or less than about 4degrees, or less than about 3 degrees, or less than about 2 degrees, orless than about 1 degree.

In some cases, light exiting the optical waveguide 120 received andaligned by the waveguide alignment feature 115 propagates along anoptical path from the input surface 132 to the output surface 136, suchthat the redirected light 150 has a minimum beam size (e.g.cross-sectional area) located near the output surface 136. Forembodiments employing single-mode waveguides, the waist of theredirected beam may be located near the output surface. In oneparticular embodiment, the input light 140 is a divergent light beam,and the redirected light 150 is a substantially collimated light beam,the collimation being limited by diffraction characteristic of the beamsize.

The reflective surface 134 can be any suitably shaped reflector capableof redirecting the input light 140 having a first divergence, to aredirected light 150 having a second divergence that is smaller than thefirst divergence. In various embodiments, the curved reflective surface134 may be a toroidal surface, or an elliptical surface, for example. Acurved intersection of the surface 134 with the XZ plane can bedescribed or accurately approximated by an arc 134 a having a radius ofcurvature “R” measured from a center 105 of the circular arc 134 a. Thearc center 105 lies on a line that bisects the redirection angle ϕbetween the input axis 142 and the redirected axis 152. The surface 134is further characterized by an axis of revolution 106, disposed in theXZ plane, and intersecting the input axis 142 at a geometrical focus108. The geometrical focus 108 is one focus of an ellipse, a portion ofwhich is best approximated by arc 134 a. The axis of revolution 106 isnon-parallel and tilted with respect to the redirected axis 152 and/orthe output axis 156 as shown in FIG. 1. For example, a toroidal orellipsoidal surface 134, can be generated, e.g., where the input axis142 intersects the surface 134, by revolving the arc 134 a about theaxis of revolution 106 (i.e., out of the XZ plane). The geometricalfocus 108 is one optical focal length, f, from the optical focal point107. The output surface 136 may be located one focal length, f, from theintersection of the input axis 142 and the curved reflective surface134.

The focal length, f, can be measured from focal point 107 to theintersection of the input axis 142 and the arc 134 a is less than theradius of curvature, R, and can be characterized by the expression:

${R = {\frac{2f}{\tan \left( \frac{\pi - \varphi}{2} \right)}\sqrt{{\tan \left( \frac{\pi - \varphi}{2} \right)}^{2} + 1}}},$

where f is the optical focal length and ϕ is the interior angle betweenthe input axis and the redirected axis. For example, when angle ϕ=90degrees (i.e., π/2) and f=0.60 mm, R=1.697 mm. In one particularembodiment, the light redirecting member 130 can be designed such thatthe path of the input light 140 and redirected light 150 travels acombined distance of 2f from the waveguide end face surface 124 to theoutput surface 136.

The reflective surface 134 can be made to be reflective by including areflective coating, such as, for example, a multilayer interferencereflector such as a Bragg reflector, or a metal or metal alloyreflector, both of which can be suitable for use with a lightredirecting member 130 that is either solid material or a hollow cavity,as described elsewhere. In some cases, for a light redirecting member130 that is a solid material, the reflective surface 134 can instead usetotal internal reflection (TIR) to redirect the input light 140. Inorder for TIR to be an effective, the connector housing 110 of unitarylight coupling unit 100 can further include an internal perimeter 119 atleast partially surrounding a cavity 118, positioned such that thereflecting surface 134 of light redirecting member 130 can be protectedfrom contamination that can frustrate TIR at the reflecting surface 134,as known to one of skill in the art.

The light redirecting member 130 can be fabricated from any suitablytransparent and dimensionally stable material including, for example,polymers such as a polyimide. In one particular embodiment, lightredirecting member 130 can be fabricated from a dimensionally stabletransparent polyimide material such as, for example, Ultem 1010Polyetherimide, available from SABIC Innovative Plastics, PittsfieldMass., or Zeonex K26r cyclic olefin polymer available from ZeonSpecialty Materials, San Jose, Calif. In some cases, the opticalwaveguide 120 can be adhesively secured in a groove of the waveguidealignment member 115. In one particular embodiment, an index matchinggel or adhesive may be inserted between the light redirecting member 130and the optical waveguide 120. By eliminating any air gap in this area,refraction and Fresnel losses may be reduced.

The center of the circular arc 105 may be located on a radiusperpendicular to the axis of revolution 106 and intersecting the pointof redirection of the central rays of the input 140 and redirected 150light beams as shown in FIG. 1. The axis of revolution 106 intersectsthe input axis 142 at a point one focal length behind the end face 124of the optical waveguide 120, for example.

The axis of revolution 106 of the curved reflective surface 134 istilted with respect to the redirected axis 152 and/or the output axis156. Additionally, the waveguide alignment member is configured suchthat the end face 124 of the optical waveguide 120 is positioned at alocation that is not a geometric focus 108 of the curved reflectivesurface 134. For example, in some embodiments, the end face 124 of theoptical waveguide 120 may be located about halfway between the curvedreflective surface 134 and the geometric focus 108. This arrangementprovides redirected light that is substantially collimated rather thanbeing substantially convergent or divergent within the light couplingunit. As previously discussed, the redirected light 150 may have asecond divergence or convergence half-angle θo. In some cases, thesecond divergence or convergence half-angle θo is less than about 5degrees, or less than about 4 degrees, or less than about 3 degrees, orless than about 2 degrees, or less than about 1 degree.

The curved reflective surface 134 may be a tilted elliptical surface ora tilted toroidal surface which very closely approximates a tiltedelliptical surface, wherein tilted refers to an tilt angle between theaxis of revolution of the surface with respect to the redirected oroutput light beam axis 152, 156. FIG. 2A depicts an elliptical crosssection of a reflector 200 illustrating the relationship between theeccentricity of the ellipsoid and the desired reflection angle, ϕ. Theeccentricity of the ellipse can be defined according to its major andminor axis (a and b) as:

$ɛ = {\sqrt{1 - \left( \frac{b}{a} \right)^{2}}.}$

In this design, the eccentricity depends on the desired reflectionangle, ϕ:

${ɛ = {\sin \left( \frac{\varphi}{2} \right)}}.$

Thus, for a 90-degree reflection (ϕ=90 degrees) the eccentricity shouldbe 1/√{square root over (2)}.

FIGS. 2A and 2B depict an elliptical cross section of a reflectorillustrating the relationship between the geometrical focus 210 and thereflective surface 234. FIG. 2B shows an elliptical cross section of areflector 200 wherein the light source 224 (e.g., the end faceof thewaveguide) is at the geometric focus 295 of the surface 234. Thegeometrical focus 295 of the ellipsoidal surface 234 is on the axis ofrevolution 206. FIG. 2B illustrates convergence of the reflected lightwhen the light source 224 is positioned at a geometric focus 295 of thesurface 234, as is characteristic of an ellipsoidal surface. Lightemitted from the geometric focus 295 on the axis of revolution isreflected by the surface 234; the reflected light converges to acomplementary geometric focus 295′ on the axis of revolution 206.

In contrast, FIG. 2A illustrates a scenario in which the light source224 is not located at a geometrical focus 295 on the axis of revolution206 but located one optical focal length from the surface 234 and onefocal length away from the geometric focus 295. As shown in FIG. 2A whenthe light source 224 is not located at the geometrical focus 295, but islocated midway along the input axis between geometric focus 295 and thesurface 234, the reflected light is substantially collimated at thecomplementary focus point 295′. The desired reflection angle 280 iscontrolled by selecting an appropriate angle for the axis of rotationrelative to the input axis.

FIG. 3A shows a schematic cross-sectional view of a connector assembly300, according to one aspect of the disclosure. Each of the elements100-160 shown in FIG. 3A correspond to like-numbered elements 100-160shown in FIG. 1, which have been described previously. For example,optical waveguide 120 of FIG. 3A corresponds to optical waveguide 120 ofFIG. 1, and so on. In FIG. 3A, connector assembly 300 includes a firstunitary light coupling unit 100 and a second unitary light coupling unit100′ that are coupled together such that mating surfaces 112, 112′ areadjacent each other; alignment features 114 and 116 are aligned withalignment features 116′ and 114′, respectively; and the output surface136 of first unitary light coupling unit 100 is proximate to and facingthe output surface 136′ of second unitary light coupling unit 100′. InFIG. 3A, each of the first unitary light coupling unit 100 and a secondunitary light coupling unit 100′ are hermaphroditic coupling units,which can be mated to each other to enable a low-loss opticalconnection. The connector assembly 300 is configured so that lightexiting the first optical waveguide 120 enters the second opticalwaveguide 120′ after being redirected by the reflective surface 134,134′ of the first and second unitary light coupling units 100, 100′.

The light exiting the first optical waveguide propagates a firstpropagation distance (f+f+f′+f′) between the waveguide end face 124 ofthe first light coupling unit 100 and the end face 124′ of the secondlight coupling unit 100′, the propagation distance (f+f+f′+f′) beingsubstantially equal to two times a sum of the focal length f of thefirst unitary light coupling unit and the focal length f′ of the secondunitary light coupling unit. In some cases, the focal length “f′” of thefirst unitary light coupling unit 100 is substantially equal to thefocal length “f” of the second unitary light coupling unit 100′. In somecases, the first optical waveguide 120 comprises a first multimodeoptical fiber and the second optical waveguide 120′ comprises a secondmultimode optical fiber. In other cases, the first optical waveguide 120comprises a first single mode optical fiber and the second opticalwaveguide 120′ comprises a second single mode optical fiber.

FIG. 3B shows a perspective schematic view of light paths through theconnector assembly 300 of FIG. 3A obtained by ray tracing, according toone aspect of the disclosure. In the embodiment shown in FIG. 3B, thefirst and second reflective surfaces 134, 134′ are right angle toroidalmirrors. In FIG. 3B, first optical waveguide 120 injects first inputlight 140 which is reflected from first toroidal reflector 134 as firstredirected light beam 150. First redirected light beam 150 passesthrough first output surface 136 of first light redirecting member 130and enters second light redirecting member 130′ through second outputsurface 136′ as second redirected light beam 150′. Second redirectedlight beam 150′ is reflected from second toroidal reflector 134′ assecond input light 140′ that enters second optical waveguide 120′.

The divergence of rays 140 exiting the core of the optical waveguide 120is representative of the numerical aperture of the waveguide. The lightpropagates within the polymer of the light coupling unit and forsufficiently large reflection angles, ϕ, the reflection can occur bytotal internal reflection. In a typical connector, the light wouldpropagate within a polymer (e.g., Zeonex K26r) and for sufficientlylarge angles (ϕ, FIG. 3A), the reflection can occur by total internalreflection. The disk 136, 136′ in the center of the model represents theinterface between two connectors.

Raytracing has been used to calculate the component of the insertionloss due to aberration for an optical connector that includes awaveguide having a multimode 50 μm diameter fiber core. The tiltedellipsoidal and toroidal designs described herein provide lowerinsertion loss than previous connectors. Table 1 summarizes thecalculated insertion loss due to aberration for 90-degree reflectionsand 600 focal lengths.

TABLE 1 DESIGN INSERTION LOSS Paraboloid 0.53 dB Toroid, axis parallelto output beam 0.36 dB Tilted ellipsoid 0.27 dB Tilted toroid (45degrees) 0.24 dB

It will be appreciated from TABLE 1 that the insertion loss due toaberration of a connector assembly incorporating a tilted reflector inaccordance with embodiments discussed herein may be less than about 0.35dB, or less than about 0.325 dB, or less than about 0.3 dB or less thanabout 0.275 dB, or less than about 0.25 dB at a wavelength in a rangefrom 600 to 2000 nanometers. Measured insertion loss of the connectorassembly incorporating the tilted reflector in accordance withembodiments discussed herein can be less than about 0.4 dB.

Low-back reflection (return loss) is an attribute of high-performanceoptical connectors and adaptors. Previous design physical-contactconnectors manage back reflection by providing angle-polished waveguideend faces. FIGS. 4A and 4B are schematic diagrams that illustrateray-tracing of a light coupling unit 400 of a typical previous design.

The input surface 432 of the light coupling unit 400 is nominally normalto the central axis 422 of the optical waveguide 420. An index matchingadhesive 484 is used to optically couple the angle-cleaved waveguide endface 424 to the input surface 432. However, because the lightredirecting portion 421 of the light coupling unit 400 has a differentrefractive index than the waveguide core or the adhesive, reflectionsoccur. A large fraction of the light reflected from the input surface432 is coupled back into the waveguide core.

The curved reflective surface 434 redirects the input light toward theoutput surface 436. A small fraction of the collimated redirected lightat the output surface 436 is reflected, despite the use of a thin-filmantireflection coating 485. Because the collimated redirected beam 491impinges on the output surface 486 at normal incidence, a portion of thecollimated redirected light 491 can be reflected at the output surface436 and re-focused by the curved reflective surface 434 back into thewaveguide 420. FIG. 4A illustrates redirected light 491 impinging atnormal incidence on the input surface 432 and the antireflection(AR)-coated output surface 436 of the light coupling unit 400. FIG. 4Billustrates that light from the waveguide 420 is partially backreflected from both the input surface 432 and the AR-coated outputsurface 436 of the light coupling unit 400. The solid 499 and dashed 498lines represent two rays that originate at opposite edges of thewaveguide core. The reflected light, represented by solid 489 and dashed488 lines is strongly coupled back into the waveguide 420, forming aninverted image of the core on the end facet. These reflections at theinput and output surfaces 432, 436 can result in unacceptable backreflection in the waveguide.

In some embodiments, back reflection can be eliminated or significantlyreduced by appropriately angling the input surface and/or output surfacewith respect to the incident light, as shown in FIGS. 5A and 5B. FIGS.5A and 5B are schematic diagrams showing ray tracing of a portion of anexample light coupling unit 500 in accordance with some embodiments.

As illustrated in FIGS. 5A and 5B, in some embodiments, the normal 532′to the input surface 532 is at angle Φ with respect to the axis 522 ofthe optical waveguide 520. Therefore, the central ray of the lightreflected by the input surface 532 is reflected at an angle of 2Φ withrespect to the waveguide axis 522. Assuming the adhesive 584 is indexmatched to the waveguide core, the reflected light will not besignificantly coupled back into the waveguide core if all reflected raysfall outside of the waveguide's numerical aperture. That is, ifΦ>Θ_(NA), where Θ_(NA) is the angle associated with the numericalaperture of the fiber: Θ_(NA)=asin(NA/n_(core)), and where NA is thenumerical aperture of the fiber, and n_(core) is the refractive index ofthe waveguide core. In some embodiments, Φ>9 degrees, for example.According to some embodiments, the input surface 532 is angled withrespect to an axis 522 of the optical waveguide 520 such that less thanabout 1 percent of light reflected by the input surface 532 is coupledback into the waveguide 520.

The angled input surface 532 need not be planar, e.g., it can bespherical, cylindrical, toroidal, or other useful lens shape, providedthat the range of angles of the surface relative to the waveguide opticaxis reduces or precludes reflections back into the waveguide core. Forexample, in some embodiments, substantially all of the input light,e.g., more than about 80 percent, more than about 85 percent, or morethan 90 percent, or more than 99 percent, that is reflected by the inputsurface 532 is reflected at angles to the waveguide axis greater thanthe numerical aperture angle of the optical waveguide 520. For example,in some embodiments, less than 20 percent, less than 15 percent or lessthan 10 percent of light that is reflected by the input surface 532 iscoupled into the core of the optical waveguide 520.

Although not shown in FIGS. 5A and 5B, an antireflective coating and/orantireflective nanostructure can be applied to the input surface 532 toreduce the reflections at the interface between the adhesive 584 and thelight coupling unit 500.

Additionally or alternatively, the prescription of thetotal-internal-reflection lens formed by curved reflective surface 534can be designed as described above to redirect and collimate light 578from the optical waveguide 520 such that the redirected axis 552 of theredirected light (the redirected axis 552 lies along the path of thecentral ray of the redirected light) makes an angle, Θ, with respect tothe normal 536′ to the output surface 536 of the light coupling unit500. As a result, any light reflected from the output surface 536 isrefocused by the TIR lens 534 to a spot away from the waveguide core. Assuch, substantially all of the light that is reflected by the outputsurface 536 and focused by the TIR lens 534 falls outside the core ofthe waveguide 520 and is therefore not coupled back into the waveguide.For example, about 80 percent, about 85 percent, or about 90 percent ofthe light that is reflected by the output surface 536 and re-focused bythe TIR lens 534 falls outside the core of the waveguide. According tosome embodiments, less than 10% or even less than 1% of redirected lightthat is reflected by the output surface 536 is refocused by the curvedreflective surface 534 into the core of the waveguide 520.

In FIG. 5B, the solid 599 and dashed 598 lines represent two rays thatoriginate at opposite edges of the waveguide core. For small Θ, aninverted image of the waveguide core is centered a distance s=2fΘ fromthe waveguide axis 522 which is the center of the core, where f is thefocal length of the TIR lens, and Θ is expressed in radians. Theredirected light, represented by solid 589 and dashed 588 lines, isreflected by the output surface 536 and is focused by the curvedreflective surface 534 to a point that is the distance, s, from a centerof a core of the waveguide 520. To reduce coupling of this reflectedimage back into the waveguide core, the distance s should be greaterthan the diameter of the waveguide core (or optical fiber mode), D. Insome embodiments the incident angle Θ is greater than D/2f and isgreater than about 2.5 degrees.

Connected light coupling unit pairs incorporating these angled input andoutput surfaces can achieve return loss values of 45 dB, 55 dB or evenbetter at 1310 nm.

In the embodiments described herein, the output surface 536 need not beplanar, e.g., the output surface 536 can be spherical, cylindrical,toroidal, or other useful lens shape, provided that the range of anglesof the surface 536 relative to the axis of the output beam reduces orprecludes reflections back into the waveguide core.

The choice of non-zero incident angles at the input and output surfacesmay involve adjustment to the design of the light coupling unit toaccommodate the associated refraction of the transmitted light. At theinput surface this refraction is typically negligible because of theindex-matched adhesive. At the output surface, the refracted beam angleinto air can be taken into account using ray-tracing techniques.

FIG. 6A shows a schematic perspective view of a unitary light couplingunit 600, according to one aspect of the disclosure. Each of theelements 600-630 shown in FIG. 6A correspond to like-numbered elements100-130 shown in FIG. 1, which have been described previously. Forexample, optical waveguide 620 of FIG. 6A corresponds to opticalwaveguide 120 of FIG. 1, and so on. In FIG. 6A, a plurality of opticalwaveguides 620 are received and aligned by waveguide alignment member615 to direct light from the optical waveguide to the light redirectingmember 630 within connector housing 610. Light coupling unit 610includes alignment features 614, 616.

FIG. 6B shows a schematic perspective view of a connector assembly 603,according to one aspect of the disclosure. The connector assembly 603can be similar to those multifiber connector assemblies shown, forexample, in U.S. Patent Application Ser. No. 61/652,478 entitled OPTICALINTERCONNECT (Attorney Docket No. 67850US002, filed May 14, 2013), whichprovides compact, reliable optical interconnects; however, the lightredirecting member 630 of the present invention provides advantages inmultifiber connector assemblies that were not previously appreciated.Connecter assembly 603 includes a first optical connector 601 having afirst unitary light coupling unit 600 and a second optical connector601′ having a second unitary light coupling unit 600′, according to oneaspect of the disclosure. Each of the first and second unitary lightcoupling units 600, 600′ can be hermaphroditic connectors, as describedelsewhere. The first and second optical connectors 601, 601′ can beprotected and supported by first and second connector frames 602, 602′,that can enable more reliable matching of the respective first andsecond alignment features 614, 616, 614′, 616′ of each of the unitarylight coupling units 600, 600′.

Each of the multifiber connector assemblies can be adapted to beinterconnected using a variety of connection schemes, as known in theart, for example as further described in copending PCT Publication Nos.WO2013/048730 entitled OPTICAL CONNECTOR HAVING A PLURALITY OF OPTICALFIBRES WITH STAGGERED CLEAVED ENDS COUPLED TO ASSOCIATED MICROLENSES;WO2013/048743 entitled OPTICAL SUBSTRATE HAVING A PLURALITY OF STAGGEREDLIGHT REDIRECTING FEATURES ON A MAJOR SURFACE THEREOF; and in U.S.Patent Application Ser. Nos. 61/652,478 entitled OPTICAL INTERCONNECT(Attorney Docket No. 67850US002, filed May 14, 2013), and 25 61/710,083entitled OPTICAL CONNECTOR (Attorney Docket No. 70227US002, filed Sep.27, 2013).

Items described in this disclosure include:

-   Item 1. A light coupling unit for use in an optical connector,    comprising:

a waveguide alignment member configured to receive and align at leastone optical waveguide; and

a light redirecting member, comprising:

-   -   an input surface configured to receive input light from an end        face of the optical waveguide;    -   a curved reflective surface configured to receive light from the        input surface propagating along an input axis and to redirect        the light received from the input surface, the redirected light        propagating along a different redirected axis; and    -   an output surface configured to receive the redirected light        from the curved reflective surface and to transmit the        redirected light received from the output surface as output        light propagating along an output axis and exiting the light        redirecting member, a curved intersection of the curved        reflective surface and a first plane formed by the input and        redirected axes having a radius of curvature, the curved        reflective surface having an axis of revolution disposed in the        first plane, wherein the axis of revolution forms a first angle        with the redirected axis, the first angle being non zero, and        the waveguide alignment member is configured such that the end        face of the optical waveguide is positioned at a location that        is not a geometric focus of the curved reflective surface.

-   Item 2. The light coupling unit of item 1, wherein the axis of    revolution is disposed at a second angle with respect to the input    axis and the first and second angles are equal.

-   Item 3. The light coupling unit of item 2, wherein the first and    second angles are about 45 degrees.

-   Item 4. The light coupling unit of item 2, wherein the first and    second angles are in a range of about 40 to about 50 degrees.

-   Item 5. The light coupling unit of item 2, wherein the first and    second angles are about 43.5 degrees.

-   Item 6. The light coupling unit of any of items 1 through 5, wherein    the curved surface is a toroidal surface.

-   Item 7. The light coupling unit of any of items 1 through 5, wherein    the curved surface is an ellipsoidal surface.

-   Item 8. The light coupling unit of any of items 1 through 7, wherein    a second divergence of the reflected light along the redirected axis    is less than a first divergence of the input light along the input    axis.

-   Item 9. The light coupling unit of any of items 1 through 8, wherein    the axis of revolution is disposed at one optical focal length, f,    measured from the input surface along the input axis and at two    focal lengths measured from the curved reflective surface measured    along the input axis, the focal length being less than the radius of    curvature.

-   Item 10. The light coupling unit of item 9, wherein the radius of    curvature, R, is:

${R = {\frac{2f}{\tan \left( \frac{\pi - \varphi}{2} \right)}\sqrt{{\tan \left( \frac{\pi - \varphi}{2} \right)}^{2} + 1}}},$

wherein ϕ is an angle between the input axis and the redirected axes.

-   Item 11. The light coupling unit of item 9, wherein the output    surface is disposed at one focal length measured along the    redirected axis from the curved reflective surface.-   Item 12. The light coupling unit of any of items 1 through 11,    wherein the light coupling unit is a unitary structure.-   Item 13. The light coupling unit of any of items 1 through 12,    wherein the input surface is substantially perpendicular to the    input axis.-   Item 14. The light coupling unit of any of items 1 through 12,    wherein the input surface is substantially perpendicular to the    output surface.-   Item 15. The light coupling unit of any of items 1 through 14,    wherein an angle between the input axis and the redirected axis is    less than 90 degrees.-   Item 16. The light coupling unit of any of items 1 through 14,    wherein an angle between the input axis and the redirected axis is    greater than 90 degrees.-   Item 17. The light coupling unit of any of items 1 through 14,    wherein an angle between the input axis and the redirected axis is    about 93 degrees.-   Item 18. The light coupling unit of any of items 1 through 17,    wherein the curved reflective surface reflects the light received    from the input surface by total internal reflection.-   Item 19. The light coupling unit of any of items 1 through 18,    wherein the input surface is angled with respect to an axis of the    optical waveguide.-   Item 20. The light coupling unit of any of items 1 through 19,    wherein the input surface is angled with respect to an axis of the    optical waveguide such that substantially all input light that is    reflected by the input surface is reflected at angles to a waveguide    axis greater than a numerical aperture angle of the waveguide.-   Item 21. The light coupling unit of any of items 1 through 20,    wherein the input surface is angled with respect to an axis of the    optical waveguide such that less than about 1 percent of light    reflected by the input surface is coupled back into the waveguide.-   Item 22. The light coupling unit of any of items 1 through 20,    wherein the input surface is angled with respect to an axis of the    optical waveguide such that input light that is reflected by the    input face is reflected an angle, Φ, wherein Φ is greater than a    numerical aperture angle, Θ_(NA), of the optical waveguide and Φ is    greater than 9 degrees.-   Item 23. The light coupling unit of any of items 1 through 22,    wherein a redirected axis of the redirected light makes an angle,    Θ>D/2f, with respect to a normal to the output surface, wherein D is    a diameter of a core the waveguide and f is a focal length of the    curved reflective surface.-   Item 24. The light coupling unit of any of items 1 through 22,    wherein a redirected axis of the redirected light makes an angle,    Θ>D/2f, and Θ>2.5 degrees, with respect to a normal to the output    surface, wherein D is a diameter of a core the waveguide and f is a    focal length of the curved reflective surface.-   Item 25. The light coupling unit of any of items 1 through 24,    wherein redirected light that is reflected by the output surface is    focused by the curved reflective surface to a point that is a    distance, s, from a center of a core of the waveguide, and s>D,    wherein D is a diameter of a core the waveguide.-   Item 26. The light coupling unit of any of items 1 through 25,    wherein less than about 10% of redirected light that is reflected by    the output surface is refocused by the curved reflective surface    into a core of the waveguide.-   Item 27. The light coupling unit of any of items 1 through 25,    wherein less than about 1% of redirected light that is reflected by    the output surface is refocused by the curved reflective surface    into a core of the waveguide.-   Item 28. A light coupling unit for use in an optical connector,    comprising:

a waveguide alignment member configured to receive and align at leastone optical waveguide; and

a light redirecting member, comprising:

-   -   an input surface configured to receive input light from an end        face of the optical waveguide;    -   a curved reflective surface configured to receive light from the        input surface propagating along an input axis and to redirect        the light received from the input surface, the redirected light        propagating along a different redirected axis; and    -   an output surface configured to receive the redirected light        from the curved reflective surface and to transmit the        redirected light received from the output surface as output        light propagating along an output axis and exiting the light        redirecting member, a curved intersection of the curved        reflective surface and a first plane formed by the input and        redirected axes having a radius of curvature, the curved        reflective surface having an axis of revolution disposed in the        first plane, wherein the axis of revolution is not parallel to        the redirected axis and wherein the waveguide alignment member        is configured such that the end face of the optical waveguide is        positioned at a location about halfway between the curved        reflective surface and a geometric focus of the curved        reflective surface.

-   Item 29. A light coupling unit for use in an optical connector,    comprising:

a waveguide alignment member configured to receive and align at leastone optical waveguide; and

a light redirecting member, comprising:

-   -   an input surface configured to receive input light from an end        face of the optical waveguide;    -   a curved reflective surface configured to receive light from the        input surface propagating along an input axis and to reflect the        light received from the input surface, the reflected light        propagating along a different redirected axis; and    -   an output surface configured to receive light from the curved        reflective surface and to transmit the light received from the        output surface as output light propagating along an output axis        and exiting the light redirecting member, a curved intersection        of the curved reflective surface and a first plane formed by the        input and redirected axes having a radius of curvature, the        curved reflective surface having an axis of revolution disposed        in the first plane, wherein the axis of revolution is not        parallel to the redirected axis and wherein the redirected light        has a redirected divergence or convergence half-angle θo that is        less than about 5 degrees.

-   Item 30. An optical connector comprising:

a connector housing; and

at least one light coupling unit as in claim 1, wherein the opticalconnector is configured to mate with a mating optical connector along amating direction, the mating direction being not parallel to the inputaxis.

-   Item 31. A connector assembly, comprising:

a first light coupling unit as in item 1 having at least one firstoptical waveguide received and aligned by the waveguide alignment memberof the first light coupling unit, the first light coupling unit matedwith a second light coupling unit as in claim 1 having at least onesecond optical waveguide received and aligned by the waveguide alignmentmember of the second light coupling unit, the output surface of thefirst light coupling unit being proximate to and facing the outputsurface of the second light coupling unit, the connector assembly beingconfigured so that light exiting the first optical waveguide enters thesecond optical waveguide after propagating through the light redirectingmembers of the first and second light coupling units.

-   Item 32. The connector assembly of item 31, wherein light exiting    the first optical waveguide propagates a first propagation distance    between the input surface of the first light coupling unit and the    input surface of the second light coupling unit, the propagation    distance being substantially equal to two times a sum of the focal    length of the first light coupling unit and the focal length of the    second light coupling unit.-   Item 33. The connector assembly of any of items 31 through 32,    wherein the focal length of the first light coupling unit is    substantially equal to the focal length of the second light coupling    unit.-   Item 34. A connector assembly, comprising:

a first light coupling unit as in claim 1 having at least one firstmultimode optical fiber received and aligned by the waveguide alignmentmember of the first light coupling unit mated with a second lightcoupling unit as in claim 1 having at least one second multimode opticalfiber received and aligned by the waveguide alignment member of thesecond light coupling unit, the output surface of the first lightcoupling unit being proximate to and facing the output surface of thesecond light coupling unit, the connector assembly being configured sothat light exiting the first optical waveguide enters the second opticalwaveguide after propagating through the light redirecting members of thefirst and second light coupling units, wherein optical insertion loss ofthe connector assembly due to aberration at a wavelength in a range from600 to 2000 nanometers is less than about 0.3 dB.

-   Item 35. The connector assembly of item 33, wherein the optical    insertion loss due to aberration is less than about 0.275 dB.-   Item 36. The connector assembly of item 33, wherein a measured    optical insertion loss is less than about 0.4 dB.-   Item 37. A light coupling unit for use in an optical connector,    comprising:

a waveguide alignment member configured to receive and align at leastone optical waveguide; and

a light redirecting member, comprising:

-   -   an input surface configured to receive input light from an end        face of the optical waveguide;    -   a curved reflective surface configured to receive light from the        input surface propagating along an input axis and to reflect the        light received from the input surface, the reflected light        propagating along a different redirected axis; and    -   an output surface configured to receive light from the curved        reflective surface and to transmit the light received from the        output surface as output light propagating along an output axis        and exiting the light redirecting member, a curved intersection        of the curved reflective surface and a first plane formed by the        input and redirected axes having a radius of curvature, the        curved reflective surface having an axis of revolution disposed        in the first plane, wherein the input surface is angled with        respect to an axis of the optical waveguide such that        substantially none of the input light that is reflected by the        input face is coupled into the waveguide.

-   Item 38. The light coupling unit of item 37, wherein the input    surface is angled with respect to an axis of the optical waveguide    such that input light that is reflected by the input face is    reflected an angle, Φ, wherein Φ is greater than a numerical    aperture, Θ_(NA), of the optical waveguide and Φ is greater than 9    degrees.

-   Item 39. The light coupling unit of any of items 37 through 38,    wherein the input surface is angled with respect to an axis of the    optical waveguide such that less than about 20% of input light that    is reflected by the input face is coupled back into the optical    waveguide.

-   Item 40. The light coupling unit of any of items 37 through 39,    wherein the input surface is angled with respect to an axis of the    optical waveguide such that less than about 5% of input light that    is reflected by the input face is coupled back into the optical    waveguide.

-   Item 41. The light coupling unit of any of items 37 through 39,    wherein the input surface is angled with respect to an axis of the    optical waveguide such that less than about 1% of input light that    is reflected by the input face is coupled back into the optical    waveguide.

-   Item 42. A light coupling unit for use in an optical connector,    comprising:

a waveguide alignment member configured to receive and align at leastone optical waveguide; and

a light redirecting member, comprising:

-   -   an input surface configured to receive input light from an end        face of the optical waveguide;    -   a curved reflective surface configured to receive light from the        input surface propagating along an input axis and to reflect the        light received from the input surface, the reflected light        propagating along a different redirected axis; and    -   an output surface configured to receive light from the curved        reflective surface and to transmit the light received from the        output surface as output light propagating along an output axis        and exiting the light redirecting member, a curved intersection        of the curved reflective surface and a first plane formed by the        input and redirected axes having a radius of curvature, the        curved reflective surface having an axis of revolution disposed        in the first plane, wherein the output light makes an angle, Θ,        with respect to a normal to the output surface, such that        substantially all light reflected by the output surface and        re-focused by the curved reflective surface falls outside a core        of the waveguide.

-   Item 43. The light coupling unit of item 42, wherein the redirected    axis is angled with respect to the output surface normal such that    about 80 percent of light reflected by the output surface and    focused by the curved reflective surface falls outside a core of the    waveguide.

-   Item 44. The light coupling unit of item 42, wherein the redirected    axis is angled with respect to the output surface normal such that    about 85 percent of light reflected by the output surface and    focused by the curved reflective surface falls outside a core of the    waveguide.

-   Item 45. The light coupling unit of item 42, wherein the redirected    axis is angled with respect to the output surface normal such that    about 90 percent of light reflected by the output surface and    focused by the curved reflective surface falls outside a core of the    waveguide.

-   Item 46. The light coupling unit of any of items 42 through 45,    wherein Θ>2.5 degrees.

-   Item 47. The light coupling unit of any of items 42 through 46,    wherein the redirected axis makes an angle, Θ>D/2f, with respect to    the output surface normal, wherein D is a diameter of a core the    waveguide and f is a focal length of the curved reflective surface.

-   Item 48. The light coupling unit of item 47, wherein redirected    light that is reflected by the output surface is focused by the    curved reflective surface to a point that is a distance, s, from a    center of a core of the waveguide, wherein s=2fΘ.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein. The use of numerical ranges by endpointsincludes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, and 5) and any range within that range.

Various modifications and alterations of the embodiments discussed abovewill be apparent to those skilled in the art, and it should beunderstood that this disclosure is not limited to the illustrativeembodiments set forth herein. The reader should assume that features ofone disclosed embodiment can also be applied to all other disclosedembodiments unless otherwise indicated. It should also be understoodthat all U.S. patents, patent applications, patent applicationpublications, and other patent and non-patent documents referred toherein are incorporated by reference, to the extent they do notcontradict the foregoing disclosure.

1-10. (canceled)
 11. A light coupling unit for use in an opticalconnector, comprising: a waveguide alignment member configured toreceive and align at least one optical waveguide; and a lightredirecting member, comprising: an input surface configured to receiveinput light from an end face of the optical waveguide; a curvedreflective surface configured to receive light from the input surfacepropagating along an input axis and to redirect the light received fromthe input surface, the redirected light propagating along a differentredirected axis; and an output surface configured to receive theredirected light from the curved reflective surface and to transmit theredirected light received from the output surface as output lightpropagating along an output axis and exiting the light redirectingmember, a curved intersection of the curved reflective surface and afirst plane formed by the input and redirected axes having a radius ofcurvature, the curved reflective surface having an axis of revolutiondisposed in the first plane, wherein the axis of revolution forms afirst angle with the redirected axis, the first angle being non zero,and the waveguide alignment member is configured such that the end faceof the optical waveguide is positioned at a location that is not ageometric focus of the curved reflective surface.
 12. The light couplingunit of claim 11, wherein the axis of revolution is disposed at a secondangle with respect to the input axis and the first and second angles areequal.
 13. The light coupling unit of claim 12, wherein the first andsecond angles are in a range of about 40 to about 50 degrees.
 14. Thelight coupling unit of claim 11, wherein the curved reflective surfaceis a toroidal surface or an ellipsoidal surface.
 15. The light couplingunit of claim 11, wherein the axis of revolution is disposed at oneoptical focal length, f, measured from the input surface along the inputaxis and at two focal lengths measured from the curved reflectivesurface measured along the input axis, the focal length being less thanthe radius of curvature.
 16. The light coupling unit of claim 15,wherein the radius of curvature, R, is:$R = {\frac{2f}{\tan \left( \frac{ - \varphi}{2} \right)}\sqrt{{{\tan \left( \frac{ - \varphi}{2} \right)}^{2} + 1},}}$wherein ϕ is an angle between the input axis and the redirected axes.17. The light coupling unit of claim 15, wherein the output surface isdisposed at one focal length measured along the redirected axis from thecurved reflective surface.
 18. The light coupling unit of claim 11,wherein the input surface is angled with respect to an axis of theoptical waveguide such that substantially all input light that isreflected by the input surface is reflected at angles to a waveguideaxis greater than a numerical aperture angle of the optical waveguide.19. A connector assembly, comprising: a first light coupling unit as inclaim 11 having at least one first optical waveguide received andaligned by the waveguide alignment member of the first light couplingunit, the first light coupling unit mated with a second light couplingunit as in claim 11 having at least one second optical waveguidereceived and aligned by the waveguide alignment member of the secondlight coupling unit, the output surface of the first light coupling unitbeing proximate to and facing the output surface of the second lightcoupling unit, the connector assembly being configured so that lightexiting the first optical waveguide enters the second optical waveguideafter propagating through the light redirecting members of the first andsecond light coupling units.
 20. A connector assembly, comprising: afirst light coupling unit as in claim 11 having at least one firstmultimode optical fiber received and aligned by the waveguide alignmentmember of the first light coupling unit mated with a second lightcoupling unit as in claim 11 having at least one second multimodeoptical fiber received and aligned by the waveguide alignment member ofthe second light coupling unit, the output surface of the first lightcoupling unit being proximate to and facing the output surface of thesecond light coupling unit, the connector assembly being configured sothat light exiting the first optical waveguide enters the second opticalwaveguide after propagating through the light redirecting members of thefirst and second light coupling units, wherein optical insertion loss ofthe connector assembly due to aberration at a wavelength in a range from600 to 2000 nanometers is less than about 0.3 dB.
 21. The connectorassembly of claim 20, wherein a measured optical insertion loss is lessthan about 0.4 dB.
 22. The light coupling unit of claim 11, wherein aredirected axis of the redirected light makes an angle, Θ>D/2f, withrespect to a normal to the output surface, wherein D is a diameter of acore the optical waveguide and f is a focal length of the curvedreflective surface.
 23. The light coupling unit of claim 11, wherein theend face of the optical waveguide is positioned at a location abouthalfway between the curved reflective surface and a geometric focus ofthe curved reflective surface.
 24. The light coupling unit of claim 11,wherein the redirected light has a redirected divergence or convergencehalf-angle θo that is less than about 5 degrees.
 25. A light couplingunit for use in an optical connector, comprising: a waveguide alignmentmember configured to receive and align at least one optical waveguide;and a light redirecting member, comprising: an input surface configuredto receive input light from an end face of the optical waveguide; acurved reflective surface configured to receive light from the inputsurface propagating along an input axis and to reflect the lightreceived from the input surface, the reflected light propagating along adifferent redirected axis; and an output surface configured to receivelight from the curved reflective surface and to transmit the lightreceived from the output surface as output light propagating along anoutput axis and exiting the light redirecting member, a curvedintersection of the curved reflective surface and a first plane formedby the input and redirected axes having a radius of curvature, thecurved reflective surface having an axis of revolution disposed in thefirst plane, wherein the input surface is angled with respect to an axisof the optical waveguide such that substantially none of the input lightthat is reflected by the input face is coupled into the opticalwaveguide.
 26. The light coupling unit of claim 25, wherein the inputsurface is angled with respect to an axis of the optical waveguide suchthat input light that is reflected by the input face is reflected anangle, Φ, wherein Φ is greater than a numerical aperture, Θ_(NA), of theoptical waveguide and Φ is greater than 9 degrees.
 27. The lightcoupling unit of claim 25, wherein the input surface is angled withrespect to an axis of the optical waveguide such that less than about20% of input light that is reflected by the input face is coupled backinto the optical waveguide.
 28. A light coupling unit for use in anoptical connector, comprising: a waveguide alignment member configuredto receive and align at least one optical waveguide; and a lightredirecting member, comprising: an input surface configured to receiveinput light from an end face of the optical waveguide; a curvedreflective surface configured to receive light from the input surfacepropagating along an input axis and to reflect the light received fromthe input surface, the reflected light propagating along a differentredirected axis; and an output surface configured to receive light fromthe curved reflective surface and to transmit the light received fromthe output surface as output light propagating along an output axis andexiting the light redirecting member, a curved intersection of thecurved reflective surface and a first plane formed by the input andredirected axes having a radius of curvature, the curved reflectivesurface having an axis of revolution disposed in the first plane,wherein the output light makes an angle, Θ, with respect to a normal tothe output surface, such that substantially all light reflected by theoutput surface and re-focused by the curved reflective surface fallsoutside a core of the optical waveguide.
 29. The light coupling unit ofclaim 28, wherein the redirected axis is angled with respect to thenormal to the output surface such that about 80 percent of lightreflected by the output surface and focused by the curved reflectivesurface falls outside a core of the optical waveguide.
 30. The lightcoupling unit of claim 28, wherein Θ>2.5 degrees.